Spacing between existing and new reinforcement
Spacing between existing and new reinforcement
(OP)
I am working replacing an old silo is replaced with a higher one (68' old and 100' new) but same diameter. At door the old silo had #4 dowels @ 3" o/c.
My question is if the old bar are cut (at top of foundation) and new dowel bars are to be placed (w/ Epoxy) in the foundation, the spacing between the old bar and the new bar will be 1.5" on o/c. Is this acceptable?
Or is there any other way?
Thank you
My question is if the old bar are cut (at top of foundation) and new dowel bars are to be placed (w/ Epoxy) in the foundation, the spacing between the old bar and the new bar will be 1.5" on o/c. Is this acceptable?
Or is there any other way?
Thank you






RE: Spacing between existing and new reinforcement
RE: Spacing between existing and new reinforcement
RE: Spacing between existing and new reinforcement
RE: Spacing between existing and new reinforcement
RE: Spacing between existing and new reinforcement
RE: Spacing between existing and new reinforcement
RE: Spacing between existing and new reinforcement
I would not recommend this approach, and always work to retain original bars where possible. Better would be to create an interface zone where you chip to expose existing bars and lap these with new, casting both into a joint zone. This, obviously, comes at a cost... But I don't think anyone can tell you that what you propose is okay based on what you've presented here.
Contact Hilti, Ramset, Powers, etc, and get their input. I think you'll find that with the right epoxy this may work, but this is beyond the standard "look it up for yourself" solution.
RE: Spacing between existing and new reinforcement
Even if you need to cut flush to the foundation you can still chip back a little bit and do a mechanical coupling to the existing bars.
RE: Spacing between existing and new reinforcement
As to use of reinforcement and spacing, what grade are the old bars? What is the purpose of the bars in question (shear friction development, tension, direct shear, or other?
In the scenario described, I would recommend using the old bars, leaving them sticking up into the new silo wall, and lapping them with new bars that extend upward. This will save substantial amounts of money. If the bars are already cut or the demolition requires it (do not let the contractor tell you it is the best or only way to go), then drilling between the old bars and using an adhesive (very few of which are actually epoxy chemistry) will work just fine. The drilled-in dowels need to extend a distance comparable to the development length of the bar in order to form a lap with the adjacent, old bars. It is not a function of the adhesive, but to assure that once the forces enter the concrete, they can fully develop into the existing reinforcement, as a (non-contact) lap splice. DO NOT rely on short adhesive embedments required by the manufacturer to fully develop the bars. These values only determine how much adhesive is required to get development, but not how much embedment is required to allow the concrete and surrounding bars to accept the load, particularly when you really do not know what is in the old foundation.